Looking like giant paving stones that have been ripped up and dumped, these slabs were once part of a crust that covered the ices of the Sputnik Planum. They are around 3 miles thick and up to 20 miles wide. They now form a mountain range protruding from the ice. There are similar mountain ranges made of dumped fragments of broken crust down the western side of Sputnik Planum.
The soft ice of Sputnik Planum was sealed off from the near vacuum and cold of space by its intact crust until it was shattered in some cataclysm, quite possibly an asteroid impact (though asteroids are called a TNOs or KBOs in Pluto’s part of the solar system). Although, we cannot rule out the possibility that some form of internal Plutonian cryogenic volcanism was responsible for the crust shattering event.
The large slabs tilted at odd angles at the left end are most likely beached on an intact shelf of crust underlying this end of Sputnik Planum, with soft ice flowing around them, like water flowing around the tetrapods of a breakwater. The fairly uniform heights of the rest of the flock of fragments further to the right suggests that they form a raft that is still floating in the ice. The differing surface textures of the blocks suggest that some are floating with the original landscape facing up, while others are upside down.
The pattern of Rayleigh-Benard convection cells of Sputnik Planum appears to continue underneath the raft of crust fragments. Convection cannot happen under the raft because by covering the ice the slabs prevent the surface cooling that drives convection. If convection cells are pushing under the raft it is likely the result of a general northerly flow of the ice of Sputnik Planum. Further north-east along the coast it is clear that Sputnik Planum ice is flooding onto the land. The same northerly flow must have carried this raft of crust fragments along and is probably still trying to push them along the shore, although they seem to have gotten stuck in a bay at the raft’s north-eastern end. The noise as these titanic blocks bump and grind along along the shore must be phenomenal.
There is a zone between the large 5-20 mile sized fragments and the shore (marked by green broken lines) which is filled with much smaller floating debris, of the same kind as fills most of the spaces between the large chunks. Here the soft Sputnik Planum ice must be too shallow for the large chunks to float any closer to shore. There is one area of exposed Sputnik Planum ice within this shallow zone looking like a lake about 5 miles wide and 18 miles long. Here it may be that the underlying ice found a gap in the floating debris wide enough for convection to get going, so that the radial motion at the surface of the convection cell is sweeping debris away from the cell’s center thus clearing this patch.
There are a couple of unsolved issues with the idea of a raft of smaller floating debris between the big slabs and the shore. One is that there appears to be a cliff casting a shadow just to the right of the ‘lake’. It might be that this is a big shard of crust that was pushed far enough onto the shore to cast a shadow onto the surrounding raft of smaller debris or even that it is anomalously dark material that just happens to align with the shadows to the north-east of al-Idrisi Montes. At this image resolution it is hard to tell.
The other issue is at the left (marked with yellow dotted lines) where the color of the smaller debris becomes much darker, even though the texture and the shore-shallows/smaller debris raft-mighty debris block configuration appears to be the same. Can these dark and light materials actually be made of the same stuff? A global view might provide a clue to the answer. Everything on Pluto further north than a latitude of about +30° appears to have a thin coating of frost. Whereas the darkest terrain, like Cthulhu Regio and Krun Macula, lies close to the equator. The color of the dark section of the raft of smaller floating in the shallows is quite similar to that of the surface to the west and to the dark terrains near the equator. The dividing line or ‘frost line’ runs very close to the point where the color of the debris in the shallow zone changes from light to dark. This would imply that the dark debris on the left (between the yellow lines) is the natural color of this material and the lighter color of the debris to the right (between the green lines) has a weather related coating of white frost.
There are small patches of darker material within the lighter colored debris north of the ‘frost line’ so the full explanation of the different debris colors is probably not as simple as weather. The way that the arrangement of light colored debris on edge of Sputnik Planum facing a dark colored shore north of latitude +30° swaps over to dark colored debris facing a light colored shore south of +30°, it is almost as though Pluto set out to fool the eye.
This arrangement of a zone of shallow Sputnik Planum ice sandwiched between the shore and mountain ranges composed of multi-mile sized slabs of displaced Plutonian crust, continues all the way along the west coast of Sputnik Planum, from the al-Irdrisi Montes in the north to the Hillary Montes in the south. The difference is that from Baré Montes southward the shallow zone is not covered by a raft of debris, so light colored Sputnik Planum ice is clearly visible in a strip to the west of the angular mountains.
The 85 mile wide slab of crust that has washed up on the heavily cratered shore of Cthulhu Regio is the biggest surviving fragment of the crust that once covered Sputnik Planum. The top of this slab has a dark texture of parallel lines, that has given some the impression of a dune field. This one slab makes up nearly half the area of the Baré Montes. 85 mile wide slab of crust of the Baré Montes